Optical mounting systems, sometimes referred to as an "optical bench," are employed for mounting various optical elements and focal planes in fixed relationship with each other for various applications including remote sensing systems used in satellites. These types of applications require that the optical bench be as lightweight as possible and dictate high thermo-mechanical performance criteria. Such applications also require that the optical bench operate satisfactorily at cyrogenic temperatures. Infrared sensor systems are often subjected to operating temperatures in the regime of 150.degree. K. to 20.degree. K.
Methods for actively aligning the optical elements mounted on these optical benches at the temperatures mentioned above are not currently available. Consequently, optical alignment is achieved by iteratively adjusting the position of the optical elements at room temperature and then measuring the alignment at the operating temperature. The thermal contraction of the materials of which the optical bench is formed, especially the material used for the structure spanning the distance between optical components, must be compensated for during room temperature adjustment.
Beryllium has enjoyed widespread use in the past as the material from which optical benches are formed, especially when cryogenic operating temperatures are required. The design configuration of prior art optical benches commonly consists of an assembly of intricately machined parts which are fastened together with screws or pins. Extruded shapes are commercially available but have not been used in part because of potential problems associated with the anisotropy of beryllium material in this form (fabrication processes such as extrusion and hot pressing tend to cause alignment of the hexagonal-structured beryllium grains, which individually have anisotropic thermo-mechanical properties). Although beryllium cannot be cast to near-net shape, it can be hot-isostatically pressed to near-net shape. Hot isostatic pressing of beryllium continues to be under development and has not yet been perfected for use in optical benches.
Fabrication of larger parts becomes increasingly difficult as larger forces and processing equipment are required. The machining and stress-relieving of beryllium block, wrought or extruded stock requires chemical etching as the final step in order to remove the surface damage caused by machining. Machined surfaces which are not subsequently etched to remove surface damage sometimes induce dimensional instability and cracking. Additional surface treatment, such as passivation or anodizing, is required to retard corrosion. Also, due to the extreme toxicity of beryllium dusts or oxides, special handling procedures are required. Further, machining of intricate beryllium parts is a very time-consuming process, and the availability of beryllium metal is quite limited. The cost of beryllium metal is sufficiently high to justify collection and recycling of chips produced during machining.
From the foregoing, it is clear that it would be very desirable to fabricate an optical bench using materials which not only obviate the problems associated with manufacturing discussed above, but also increase the performance of the bench. The present invention is directed toward satisfying this need in the art.